1. Field of the Invention
This invention relates to a pneumatic radial tire having excellent cornering properties and either or both of durability and high-speed durability. More particularly it relates to a pneumatic radial tire for use in general-purpose passenger cars mainly developed for weight reduction.
2. Description of the Related Art
With the demand for energy saving, it has been attempted to improve the fuel consumption in automobiles by reducing the weight, and this in turn tends to raise the demand for weight reduction in tires. Particularly, this is true in pneumatic radial tires for use in general-purpose passenger cars.
In general, a pneumatic radial tire comprises a so-called cross belt formed by laminating at least two slant belt layers on an outer periphery of a carcass crown portion to cross cords of these layers with each other. From a viewpoint of tire weight reduction, there have been developed tires comprising a belt composed of a single slant belt layer and a circumferential belt layer(s) containing light-weight organic fiber cords arranged substantially in parallel to an equatorial plane of the tire. The tire of this type is disclosed in, for example, JP-A-62-152904 and JP-A-4-163212.
In the tires disclosed in these prior art publications, organic fiber cords having a high tensile rigidity in the circumferential direction such as aromatic polyamide fiber cords (e.g. Kevlar cord) and the like are used as a cord in the circumferential belt layer. Further, it is disclosed that the circumferential belt layer can control the pushing out of the tread portion through centrifugal force during the high-speed running to improve the high-speed durability.
Moreover, organic fiber cords widely used as a cord for a carcass ply such as polyethylene terephthalate (hereinafter abbreviated as PET) fiber cord, nylon fiber cord, polyethylene naphthalate (hereinafter abbreviated as PEN) fiber cord and vinylon (PVA) fiber cord are considerably low in tensile rigidity in the circumferential direction as compared with the aromatic polyamide fiber cord, so that they are hardly ever applied as a cord for the circumferential belt layer. Also, the use of steel cords for the circumferential belt layer is unfavorable from a viewpoint of weight reduction and the like, so that steel cords are hardly ever used in the circumferential belt layer.
When aromatic polyamide fiber cords are used in the circumferential belt layer, however, the resistance to compression fatigue is poor, so that it has been confirmed that the belt is apt to create compression breakage accompanied with buckling deformation of the belt generated during the severe cornering.